JP3149599B2 - Lead screw device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a feed screw device used as driving means for a moving stage, a moving table and the like.

[0002]

2. Description of the Related Art When a tool and a workpiece are relatively moved by a machine such as a lathe, or a specimen is moved to a predetermined position by an observation device such as a microscope, the tool is fed as a means for this movement. Screw devices are used. FIG. 3 is a schematic view showing the configuration of the conventional feed screw device 10 and shows an example in which it is used as a tool moving means of a machine tool. The feed screw device 10 includes a male screw 11, a nut 12 having a female screw to be screwed with the male screw 11, and a coupling 16.
Drive means 1 such as a motor for rotating screw 11 through
3 is provided. The male screw 11 is fixed to a base (not shown) via a bearing 15, and the nut 12 is provided with a table 14. In the figure, male screw 1
1 is omitted from the drawing.

In the feed screw device 10 having such a configuration,
When the driving means 13 is driven to rotate the screw 11, the nut 12 makes a linear motion along the longitudinal direction of the male screw 11 (the direction of the arrow P). Therefore, for example, if the tool 52 such as a cutting tool is installed on the table 14 and the workpiece 52 is fixed to the base or the like, the tool 51 can be moved with respect to the workpiece 52. The processing position can be moved.

[0004]

By the way, in the feed screw device having the above-mentioned structure, a frictional force is generated between the male screw and the "thread formed on the nut" screwed to the male screw. Therefore, the following three problems have arisen due to this frictional force. A first problem is that a rotational driving force required to drive a male screw by the frictional force increases. When the rotational driving force is increased, the driving force of the driving means must be increased, causing problems such as an increase in the size of the driving means and an increase in power consumption. A second problem is that frictional heat is generated in proportion to the product of the relative speed between the male screw and the nut and the frictional force. The frictional heat may cause seizure between the male screw and the female screw of the nut, or the male screw may thermally expand to lower the movement accuracy.
In addition, when the frictional heat is generated, the temperature around the feed screw device may be increased. If the device is to be used in a constant environment, it is necessary to install an air conditioner to keep the temperature constant. A third problem is that since the frictional force is provided on the male screw and the nut, the screw is worn. When wear occurs, a gap is formed between the external thread and the internal thread, and when the nut (table) moves, play such as vibration occurs, which causes a problem that the positioning accuracy of the table decreases and the table cannot move straight.

As a feed screw device having a small frictional force, there is known a feed screw device provided with a ball screw in which a male screw and a nut operate via a hard sphere (ball). In such a device, since the frictional resistance is reduced by the rolling motion of the hard sphere, the frictional force acting between the male screw and the female screw is reduced, and the above-mentioned problem is solved. However, when a force in the linear motion direction (P direction) is applied to the nut from the outside, the screw rotates through the hard sphere, so that the table cannot be fixed at a fixed position ( Self-lock is not possible). Therefore, it is necessary to separately provide a lock mechanism or the like for stopping the rotation of the table or the male screw. As a result, there has been a problem that the configuration of the feed screw device is complicated.

The present invention has been made in view of the above problems, and has as its object to provide a feed screw device that can reduce the frictional force between a male screw and a nut with a simple configuration.

[0007]

According to the present invention, there is provided, in accordance with the present invention, a first screw and a second screw threadedly engaged with the first screw. In a feed screw device having a moving body that moves to a position above, ultrasonic vibration applying means for applying ultrasonic vibration to at least one of the first screw and the second screw is provided.

[0008]

It is known that when ultrasonic vibration is applied to a solid, the friction coefficient of the surface of the solid decreases. In the present invention, a first screw (male screw) and a second screw screwed to the first screw are used.
The ultrasonic vibration is applied to at least one of the nuts on which the above-mentioned screw (female screw) is formed, so that the side to which the vibration is applied has a reduced friction coefficient on its surface (that is, the contact surface with the other side). As a result, the frictional force generated between the male screw and the female screw when the feed screw device is driven is reduced to about several tenths as compared with the case where no ultrasonic vibration is applied. Since the effect of reducing the frictional force occurs only when the ultrasonic vibration is applied, by stopping the application of the ultrasonic vibration, the surface of the male screw or the female screw can be returned to the original friction coefficient. Therefore, if the frictional force in a state where ultrasonic vibration is not applied is set to a value that does not cause rotation of the male screw or movement of the nut even when an external force is applied, self-locking is possible and the nut is fixed. Can be maintained at the position of.

The material of the male screw or female screw (nut) that imparts ultrasonic vibration is not particularly limited as long as the material transmits ultrasonic vibration. Metal, glass, ceramic, or the like may be used. it can. The ultrasonic vibration applied to the male screw or the nut may be longitudinal vibration along the longitudinal direction of the male screw or torsional vibration along the rotation direction of the male screw.

[0010]

Embodiment 1 FIG. 1 (a) is a schematic configuration diagram showing one embodiment of the present invention, and is configured to apply ultrasonic vibration to a male screw. In the figure, components having the same functions as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The feed screw device 1 of the present embodiment includes an oscillator 2 that outputs high-frequency electric vibration, a bolted Langevin-type electrostrictive vibrator 3 that receives the high-frequency electric vibration and generates ultrasonic vibration, and one end of the vibrator 3. A horn 4 which is screwed to increase the amplitude of the ultrasonic vibration, a male screw 5 attached to the tip of the horn 4, a nut 12 having a female screw (not shown) screwed to the male screw 5, a nut 12 Table 14 and coupling 16 and connecting member 8 attached to
And a driving means 13 including a motor for rotating the screw 5 through the motor. In this embodiment, the oscillator 2 and the vibrator 3
The horn 4 constitutes an ultrasonic vibration applying means 17, and applies ultrasonic vibration to the male screw 5. The material of the male screw 5 is carbon steel (S45C) and the nut 1
The material of No. 2 was a bronze alloy (BC3). The horn 4 and the male screw 5 are formed integrally with the horn 4 and the male screw 5 by cutting flanges 6 and 7, respectively. And
The feed screw device 1 is fixed to a base (not shown) via bearings 15 at these flanges 6 and 7.

When other components are mounted on the male screw 5, in order to suppress the attenuation of the ultrasonic vibration transmitted to the male screw 5, the mounting position must be set to a node of the amplitude of the ultrasonic vibration (wave node: vibration node). ) Is desirable. Also in the present embodiment, the wavelength of the ultrasonic vibration applied to the male screw 5 is assumed in advance, and the formation positions of the flanges 6 and 7 are adjusted based on the wavelength to determine the amplitude of the ultrasonic vibration transmitted to the horn 4 and the male screw 5. (See FIG. 1B). Since the end of the male screw 5 becomes an antinode of the amplitude, the attenuation of the ultrasonic vibration is reduced by attaching the cup-shaped connecting member 8 to the above-mentioned flange 7 and connecting the connecting member 8 to the coupling 16. The driving force from the driving means 13 is suppressed and transmitted to the male screw 5. In addition, if ultrasonic vibration is given to the external thread 5, it is not necessary to limit the formation position of the flanges 6 and 7 to the node of the said amplitude. However, if a flange is provided at a position other than a node, that portion becomes a node, so that the frequency of ultrasonic vibration or the like is changed in order to obtain a desired effect. Therefore, the frequency of the ultrasonic vibration is set again, which is troublesome. Further, if the ultrasonic vibration can be supported so as not to be attenuated, it is not necessary to particularly provide a flange.

The length L of the external thread 5 is λ for the wavelength when the ultrasonic wave is fixed, C for the sound speed when the ultrasonic wave is fixed, and f for the frequency of the high-frequency electric vibration output from the generator 2. Is set to satisfy the following equation.

[0013]

(Equation 1)

When the length L of the male screw 5 satisfies the above expression, a standing wave is generated in the male screw 5 by ultrasonic vibration, so that the friction coefficient of the surface can be reduced efficiently. However, even when the length L of the male screw 5 does not satisfy the formula, if ultrasonic vibration is applied to the male screw 5, the coefficient of friction of the surface of the male screw 5 decreases. Therefore, it is not necessary to limit the length L to a value that satisfies the equation. In the present embodiment, the frequency f of the high-frequency electric vibration output from the oscillator 2
And the length L of the screw 5 was set based on the sound speed C determined by the material of the male screw 5 so that the above was satisfied.

In the feed screw device 1 configured as described above, the high-frequency electric vibration (frequency 20 kHz) generated by the oscillator 2
When z) is applied to the bolted Langevin type electrostrictive vibrator 3, the vibrator 3 generates mechanical vibration (ultrasonic vibration). The ultrasonic vibration generated here has the vibration frequency
It is about 20 kHz, transmitted to the horn 4 and its amplitude is increased several times before being transmitted to the male screw 5. Since the length L of the male screw 5 satisfies the expression as described above, a standing wave (standing wave) is generated when the ultrasonic vibration is transmitted,
The coefficient of friction on the surface of the male screw 5 becomes smaller. In the embodiment, the length L of the screw 5 is set so as to satisfy the above expression. However, the ultrasonic vibration may be simply applied to the male screw 5 without satisfying the expression as described above. Also in this case, the effect of reducing the friction coefficient on the surface to which the ultrasonic vibration is applied can be obtained. However, the effect is less than when a standing wave is generated.

When the driving means 13 is driven in a state where ultrasonic vibration is applied to the male screw 5, this driving force is applied to the coupling 1
6, transmitted to the screw 5 via the connecting member 8. As a result, the male screw 5 rotates, so that the nut 12 moves in any direction of the arrow P according to the rotation direction of the male screw 5. At this time, the frictional force generated between the male screw 5 and the nut 12 is
Due to the decrease in the coefficient of friction of the surface of the male screw 5, it is reduced as compared with the case where no ultrasonic vibration is applied. For example, in the present embodiment, the frictional force could be reduced to about several tenths when ultrasonic vibration was not applied. Therefore, the load on the driving means 13 required to rotate the male screw 5 is smaller than in the conventional case. Further, the generation of frictional heat could be reduced as compared with the conventional case. In addition, male screw 5 and nut 1
2, the wear of the screw could be suppressed.

When the generator 2 was stopped and the application of ultrasonic vibration to the screw 5 was stopped, the friction coefficient on the surface of the male screw 5 returned to the value before the application of ultrasonic vibration. In this state, the frictional force generated between the male screw 5 and the nut 12
Is sufficient to keep the position of the table 14 fixed, and the table 14 was not inadvertently moved by an external force.

[0018]

Embodiment 2 FIG. 2 is a schematic view showing the configuration of another embodiment of the present invention, in which ultrasonic vibration is applied to a nut 23 having a female thread. In the drawing, components having the same functions as those in FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted as appropriate. The feed screw device 21 of the present embodiment includes an oscillator 2 that generates high-frequency electric vibration, a male screw 22, and a female screw (not shown) that is screwed with the male screw 22. A nut 23 also serving as a vibrator for generating sonic vibration, a table 24 attached to the nut 23, and a driving means 13 such as a motor for rotating a screw 22 via a coupling 16 are provided. In addition,
The material of the male screw 22 was carbon steel (S45C), and the material of the nut 23 was bronze alloy (BC3). The bearing 15 is attached to the male screw 22, and the feed screw device 21 is fixed to a base (not shown) via the bearing 15.
A flange 25 is integrally formed with the nut 23 by shaving or the like. As in the first embodiment, the flange 25 is provided at a position serving as a node of the amplitude of the ultrasonic vibration transmitted through the nut 23, and is set so that the ultrasonic vibration is hardly attenuated. Further, the length L2 of the nut 23 is also equal to that of the first embodiment.
Similarly, it is set so as to satisfy the equation.

In the feed screw device 21 configured as described above, the high-frequency electric vibration (frequency 26 k
Hz) is applied to the nut 23, the nut 23 generates mechanical vibration (ultrasonic vibration). The ultrasonic vibration generated here has a vibration frequency of about 26 kHz. Since the length L2 of the nut 23 satisfies the equation as described above, a standing wave is generated when the ultrasonic vibration is transmitted. As a result, the friction coefficient of the surface of the screw (the contact surface with the male screw 22) formed on the nut 23 is reduced. When the driving means 13 is driven to rotate the screw 22 in this state, the nut 23 moves in any direction of the arrow P according to the rotation direction of the male screw 22. At this time, the friction force generated between the male screw 22 and the female screw of the nut 23 is
Due to the decrease in the coefficient of friction of the internal thread surface, it decreases as compared with the case where ultrasonic vibration is not applied.

When the ultrasonic vibration of the nut 23 is stopped by stopping the generator 2, the friction coefficient of the screw surface formed on the nut 23 returns to the value before the ultrasonic vibration is applied, so that an external force is applied. , The table 24 is less likely to move carelessly. In each embodiment, a driving means is provided, and the male screw is rotated by the driving means to move a nut (table) on which a female screw is formed. However, if ultrasonic vibration is applied to either the male screw or the female screw, the frictional force generated between the female screw and the female screw becomes smaller as described above, so the nut (table) is manually moved. It is also possible. Therefore, for example, only when it is desired to move the nut (table), ultrasonic vibration is applied to one of the male screw and the nut and manually moved by a predetermined amount, and then the application of the ultrasonic vibration is stopped. The nut (table) can be fixed to the table. In this case, there is an advantage that the configuration of the device is simplified because the driving unit is not required.

[0021]

According to the present invention, at least one of the screws formed on the male screw or the nut is subjected to ultrasonic vibration to reduce the friction coefficient of the surface, so that the male screw is formed when the feed screw device is driven. The frictional force generated between the screw and the screw can be reduced. Therefore, the rotational driving force for driving the male screw can be reduced, and the driving unit can be reduced in size and power consumption can be reduced. Further, since the generation of frictional heat due to the frictional force can be suppressed, it is possible to prevent seizure between the male screw and the female screw, and also to reduce the possibility of increasing the ambient temperature. Further, since the wear of the thread portion of the male screw or the nut is suppressed, a gap is hardly formed between the two, and there is no backlash due to vibration or the like during driving. for that reason,
A decrease in positioning accuracy can be prevented, and linear movement can be accurately performed.

Further, by stopping the application of the ultrasonic vibration, the frictional force can be returned to a value when no vibration is applied, so that the frictional force between the two when the vibration is not applied can be appropriately set. With this frictional force, the relative position between the male screw and the nut can be maintained in a predetermined state. Therefore, there is no need to provide a lock mechanism or the like for preventing the relative position between the male screw and the nut from changing, and there is an advantage that the configuration of the device does not need to be complicated.

[Brief description of the drawings]

1 shows an embodiment of a feed screw device in which ultrasonic vibration is applied to a male screw, FIG. 1 (a) is a schematic configuration diagram thereof, and FIG. 1 (b) is a diagram of ultrasonic vibration transmitted through a male screw. It is a schematic diagram showing a situation.

FIG. 2 is a schematic configuration diagram showing an embodiment of a feed screw device in which an ultrasonic vibration is applied to a female screw.

FIG. 3 is a schematic view showing a configuration of a conventional feed screw device.

[Description of Signs of Main Parts]

 REFERENCE SIGNS LIST 1 feed screw device 2 generator 3 oscillator 4 horn 5 male screw (first screw) 6 flange 7 flange 8 connecting member 10 conventional feed screw device 11 male screw 12 nut (moving body) 13 drive means 14 table 16 cup Ring 21 Feed screw device 22 Male screw (first screw) 23 Nut (moving body) 24 Table 25 Flange

Claims (1)

(57) [Claims] 1. A feed screw device comprising: a first screw; and a moving body including a second screw engaged with the first screw and moving relatively to the first screw. A feed screw device comprising an ultrasonic vibration applying means for applying ultrasonic vibration to at least one of the first screw and the second screw.